Powerline communications technologies use existing electrical power distribution infrastructure in order to implement machine to machine communication. Such powerline communications technologies are attractive because infrastructure exists to distribute the communication signals. However, using power distribution infrastructure poses challenges not present in other wired networking technologies, where dedicated infrastructure is provided specifically for data communications, e.g., as in ethernet communications or in data communications using telephone lines or coaxial cable.
One category of challenge in powerline communication is the amount of electrical noise in the powerline infrastructure, which in addition to making data communication signal more difficult also poses considerable risk of damage to the sensitive integrated circuits used as transceivers to transmit and receive data signals over the powerline infrastructure.
FIG. 1 depicts a portion of a prior art approach to protecting a transceiver 15 from overvoltage, such as from powerline noise from a power line 21 or from Electro Static Discharge (ESD). In FIG. 1, a pair of shunting diodes 17 are connected back to back with respective opposite terminals of each diode connected to one of two different voltage references. In FIG. 1, one reference is a Vdd reference 24 and the other is a ground 25. A resistor 19 couples to a node 18 defined as the common junction of back-to-back diode pair 17. Resistor 19 couples a powerline connection 21 to the common junction of back-to-back diode pair 17 (identified as node 18 in FIG. 1). In some situations, transceiver 15 may be a differential mode transceiver such that the structures described above may be duplicated for a separate transceiver channel, generally identified as channel 27, without its constituent components specifically identified. When the diodes are forward biased, they present a low resistance connection to power supply rails, such as ground and Vdd. Therefore, noise energy is largely absorbed by resistor 19 because transceiver 15 has high impedance inputs compared with resistor 19.
It is generally desirable to reduce noise at the input of the transceiver to improve communications.